Broadband solid-state power amplifiers (SSPA) with high power and high efficiency are of interest for many radio frequency (RF) applications as an attractive alternative to vacuum tube technologies. For instance, applications such as ultra-wideband (UWB) communication systems, satellite communication systems, commercial communications, and radar transmitters, are but a few systems that can benefit from high power and high efficiency broadband SSPAs. However, power amplifier technologies can suffer from various limitations such as, for example, limited bandwidth, limited output power, excessive losses, inconvenient or unfortunate sizing or configuration, etc. Power combining can be employed to overcome many of these limitations, but in certain instances, it may involve additional consideration. For example, broadband high efficiency amplifiers can be demonstrated by combining output power from a number of solid-state devices at microwave and millimeter-wave frequencies.
For instance, combining power (and dividing power) in high frequency systems can be performed using conventional power dividers. A device for dividing and/or combining high frequency signals is called a power divider or a power combiner. As an example, a power divider can be a circuit or circuit element for dividing input power from an input port and directing it to output ports in an RF circuit. Typically, a power divider can divide power at a predetermined ratio with minimal power loss and with isolation between the output ports. In this manner, the power divider can prevent a change in circuit characteristic due to mutual influence of adjacent ports. In a similar manner, a power divider can be used as a power combiner by switching usage of input and output ports.
As a result, for applications that require a high-power, high-efficiency, broadband, SSPA, due to the aforementioned limitations of single amplifiers, amplifiers are typically combined in power dividing/combining networks to provide high power. Such techniques can be employed as a combiner, for instance, in a transmitter for combining signals from a number of low power devices to form a high power signal for transmission through a single antenna. For example, an amplifier for amplifying wireless signals can have the limitation of a low output power level as previously mentioned. To overcome this limitation, a plurality of low or medium output amplifiers can be connected in parallel to obtain a desired high power output for transmission of the wireless signals. In other implementations as a divider, a signal from a single source, such as an antenna, can be divided into a number of signals, such as for exciting a number of corresponding satellite or radar antennas. Thus, parallel, multiple-way, waveguide-based power dividing/combining network can provide many advantages for broadband RF applications.
However, conventional broadband power-combining techniques for the design of broadband high-power SSPAs demonstrate that challenges remain. For instance, among various types of combiners, radial waveguide spatial power combiners can reduce spill-over losses while demonstrating high power-combining efficiency. In addition, equal power distribution with broadband performance can be achieved in part by appropriate placement of coaxial probes in the radial waveguide. Nonetheless, while such topologies can facilitate providing broadband capability, low loss, good heat sinking capability, and ease of fabrication, practical limitations such as size and performance limitations can limit the number of ports that can be provided in radial waveguide spatial power combiners.
For example, with an increasing number of power-dividing ports, the radius of a radial waveguide or conical line will increase, which can cause higher order modes in the radial waveguide or conical line power dividing cavity due to discontinuities, and which can be difficult or impractical to suppress effectively. These effects can be exacerbated when the number of power-dividing ports of power dividers increases to more than about twenty or thirty. As a result, beyond this conventional limitation the performance of these types of power dividers can deteriorate due to the higher order modes.
The above-described deficiencies of today's power-combining and power-dividing techniques are merely intended to provide an overview of some of the problems of conventional systems, and are not intended to be exhaustive. Other problems with conventional systems and corresponding benefits of the various non-limiting embodiments described herein may become further apparent upon review of the following description.